In recent years, LEDs, cold cathode tubes configured by cold cathode fluorescent tubes, organic ELs, and the like have been gathering attention as novel light sources that would replace incandescent lamps and fluorescent lamps configured by hot cathode fluorescent tubes. In particular, planar light emitting devices, such as organic EL panels, are expected to serve as illumination devices that exhibit an unprecedented effect with the characteristics of the above-described novel light sources fully exploited.
Here, a planar light emitting device has a structure including planar light emitting elements that emit light in a planar manner. For example, such a planar light emitting device may be an LED tile in which LEDs being planar light emitting elements are arranged in a planar manner, or in which LEDs and a diffusion plate are combined with each other. Further, other planar light emitting device may be an organic EL element including wiring for receiving power from an external source, and additionally including a control circuit, a circuit board equipped with the control circuit and the like (PCB), and a housing.
Among planar light emitting elements, an organic EL element is characterized by planar light emission, and additionally by being thin, lightweight, and emitting soft diffused light. In general, such an organic EL element is formed by base members such as a glass substrate, a transparent resin film, and a metal sheet. On an element-formed surface of the substrate, two thin-film electrode layers opposing to each other, one or both of which being light-transmissive, and an organic functional layer interposed between the thin-film electrode layers are formed. Thus, an organic EL element is obtained. Further, in general, in order to prevent entry of moisture or oxygen into the element from the outside, the element is further sealed, thereby manufactured as an organic EL tile including the base member. When power is applied between the electrode layers, the electrically excited electrons and holes recombine with each other in the organic EL element, whereby the organic EL tile emits light.
Further, a planar light emitting device which includes such an organic EL tile provided with wiring for receiving power from an external source is referred to as an organic EL panel. The organic EL panel generally includes an anode pad conducted to an anode thin-film electrode layer so as to be equipotential. Hereupon, the anode thin-film electrode layer is the anode and one of the above-described thin-film electrode layers. Additionally, the organic EL panel includes a cathode pad conducted to a cathode thin-film electrode so as to be equipotential. Hereupon, the cathode thin-film electrode is the cathode and the other one of the above-described thin-film electrode layers. The organic EL panel is formed by soldering leads to these pads (the anode pad and the cathode pad) formed film-like on an element-formed surface, or by mounting an element-dedicated circuit board such as a flexible printed circuit (FPC) or other wiring members to these pads. Note that, the terms used herein such as an organic EL tile and an organic EL panel are defined in International Standards IEC 62868.
In the above-described FPC, in general, at least one continuous equipotential region is formed on one or both of the surfaces of a resin-made insulating film, which is the base member and made of polyimide or the like. This equipotential region is formed by bonding a patterned metal film such as copper foil or aluminum foil, to achieve electrical conduction at low resistance.
A planar light emitting device including such an FPC is disclosed in Patent Document 1. The organic EL illumination device disclosed therein includes, on a glass substrate, an organic EL element and a plurality of anode terminal electrodes and cathode terminal electrodes for evenly supplying current to the organic EL element. The organic EL illumination device includes a circuit board having a circuit provided with anode wiring corresponding to the position of the anode terminal electrodes, and a circuit provided with cathode wiring corresponding to the position of the cathode terminal electrodes.
Further, Patent Document 2 discloses, as such a planar light emitting device, an EL light source body capable of stably supplying power while securing the mechanical strength. The EL light source body is structured by aligning and overlaying (fitting), in sequence, a front surface case disposed on the light-emitting front surface side, an EL element housed in the front surface case and emits light, a circuit board that supplies power to the EL element, and a back surface case. The front surface case includes a planar supporting part that houses the EL element, and a frame. The circuit board includes a terminal part, and a wiring part that supplies power to the EL element through a wiring pattern and connection pattern. The back surface case fits into the front surface case so as to cover the back surface opposite to the front surface from which light is emitted, and includes a covering part and a frame that houses therein the EL element.